Device for measuring distance between headrest and head, method for measuring distance between headrest and head, headrest position adjusting device, and headrest position adjusting method

ABSTRACT

A headrest position adjusting device  100  includes a distance measuring device  10  and a drive motor unit  30 , and the distance measuring device  10  includes a plurality of sensing electrodes  11  to  15  and a detecting circuit  20 . The detecting circuit  20  includes a plurality of capacitance sensing circuits  21  to  25  connected one-to-one to the sensing electrodes  11  to  15  and an arithmetic processing circuit  28 , and the drive motor unit  30  includes a motor driving circuit and a drive motor. Based on the detected capacitance values, the detecting circuit  20  calculates a distance calculation angle θ formed by points representing the positions and output values of the sensing electrodes  15  and  11  located at the highest and lowest positions and a point representing the position and output value of the largest output value, and thereby measures an electrode-head distance L. A position adjusting operation for a headrest  43  is performed based on the measurement result.

TECHNICAL FIELD

The present invention relates to a device for measuring the distancebetween a headrest and a head for measuring and utilizing the distancebetween a headrest provided on a seat of a vehicle such as an automobileand a head, a method for measuring the distance between a headrest and ahead, a headrest position adjusting device, and a headrest positionadjusting method.

BACKGROUND ART

Conventionally, a vehicle headrest device (for example, see PatentDocument 1 (pp. 6-8, and FIGS. 1-4)) is known as a technique foradjusting the position of a headrest provided on a seat of a vehiclesuch as an automobile, etc. When this vehicle headrest device moves thefront portion of the headrest in a direction to be fully opened, an ECUof the device judges based on a detection result of a capacitance sensorthat the front portion of the headrest has come close to the head of avehicle occupant and stops the front portion of the headrest.

The ECU judges that the front portion of the headrest has come close tothe head of the vehicle occupant based on an absolute capacitance changefrom a reference capacitance value of the capacitance sensor or based onan amount of change of the capacitance value.

A vehicle occupant protecting device (for example, see Patent Document 2(pp. 3-6, and FIGS. 1-5)) is a technique for moving a headrest, which ismovable forward with respect to the vehicle, to a pre-crash phase beforean object crashes into the vehicle from behind. This device controls theamount to move the headrest frontward based on how a capacitance sensedby a capacitance sensor changes.

A vehicle occupant sensing system (for example, see Patent Document 3(pp. 3-5, and FIGS. 1-4)) generates a weak electric field around aplurality of strip-shaped antenna electrodes which are provided in ahorizontal state in a backrest (or a seat back) of a seat with a gapprovided therebetween in the vertical direction. The system detects acurrent flowing through the antenna electrodes based on the weakelectric field.

Then, the system extracts the shoulder line of the vehicle occupantsitting on the seat based on the detected current, senses the positionof the head based on the shoulder line, and sends data based on thesensing result to an air bag device. In this way, the system sets theair bag of the air bag device to a deployable or non-deployable state.

CONVENTIONAL ART DOCUMENTS Patent Documents

Patent Document 1: JP No. 4018112

Patent Document 2: JP2007-131026A

Patent Document 3: JP No. 3347069

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, the vehicle headrest device disclosed in Patent Document 1identified above and the vehicle occupant protecting device disclosed inPatent Document 2 identified above have to move the headrest constantlyin order to determine the distance between the head of the vehicleoccupant and the headrest. Moreover, if the head of the vehicle occupantmoves while the headrest is operating, the device might detect a falseamount of movement. This takes unnecessary power consumption, generatesan error in a calculation result, and makes it difficult to move theheadrest with a correct distance determination.

Furthermore, since the vehicle occupant sensing system disclosed inPatent Document 3 identified above is a system for sensing the physicalconstitution of the vehicle occupant, it cannot be applied to, forexample, a system for maintaining the distance between the headrest andthe head of the vehicle occupant.

To solve the problems of the conventional techniques described above, anobject of the present invention is to provide a device for measuring thedistance between a headrest and a head, a method for measuring thedistance between a headrest and a head, a headrest position adjustingdevice, and a headrest position adjusting method which are, with asimple configuration, capable of measuring the distance between aheadrest and a head and automatically adjusting the position of theheadrest accurately by, in particular, preventing an unnecessarymovement of the headrest.

Means for Solving the Problem

To solve the problems described above and achieve the object, a devicefor measuring a distance between a headrest and a head according to thepresent invention includes: a plurality of sensing electrodes which areprovided in a headrest provided on a seat of a vehicle for sensingcapacitances between a head of a human body sitting on the seat and theheadrest, the sensing electrodes being provided side by side along aheight direction of the headrest; a detecting circuit which detectscapacitance values which are based on the capacitances from theplurality of sensing electrodes; and distance measuring means whichmeasures an electrode-head distance indicating a distance between theheadrest and the head, in accordance with detection results detected bythe detecting circuit, wherein when the sensing electrode located at ahighest position of the headrest or the sensing electrode located at alowest position thereof among the plurality of sensing electrodes doesnot show a largest capacitance, the distance measuring means measuresthe electrode-head distance by calculating, on a two-dimensionalcoordinate system representing positions of the plurality of sensingelectrodes on its one axis and the capacitance values detected by thedetecting circuit on its other axis, a distance calculation angle formedby a line which connects a point representing the position andcapacitance value of the sensing electrode located at the highestposition of the headrest and a point representing the position andcapacitance value of the sensing electrode from which a largestcapacitance value is detected and a line which connects a pointrepresenting the position and capacitance value of the sensing electrodelocated at the lowest position of the headrest and the pointrepresenting the position and capacitance value of the sensing electrodefrom which the largest capacitance value is detected, and when thesensing electrode located at the highest position of the headrest or thesensing electrode located at the lowest position thereof shows thelargest capacitance, the distance measuring means measures theelectrode-head distance by calculating, on the two-dimensionalcoordinate system, an angle of a slope of a line which connects thepoint representing the position and capacitance value of the sensingelectrode located at the highest position of the headrest and the pointrepresenting the position and capacitance value of the sensing electrodelocated at the lowest position of the headrest.

A device for measuring a distance between a headrest and a headaccording to the present invention includes: a plurality of sensingelectrodes which are provided in a headrest provided on a seat of avehicle for sensing capacitances between a head of a human body sittingon the seat and the headrest, the sensing electrodes being provided sideby side along a height direction of the headrest; a detecting circuitwhich detects capacitance values which are based on the capacitancesfrom the plurality of sensing electrodes; and distance measuring meanswhich measures an electrode-head distance indicating a distance betweenthe headrest and the head, in accordance with detection results detectedby the detecting circuit, wherein the distance, measuring means measuresthe electrode-head distance by calculating, on a two-dimensionalcoordinate system representing positions of the plurality of sensingelectrodes on its one axis and the capacitance values detected by thedetecting circuit on its other axis, an angle of a slope of a line whichconnects a point representing the position and capacitance value of thesensing electrode from which a smallest capacitance value is detectedamong the plurality of sensing electrodes and a point representing theposition and capacitance value of the sensing electrode from which alargest capacitance value is detected among the plurality of sensingelectrodes.

A device for measuring a distance between a headrest and a headaccording to the present invention includes: a plurality of sensingelectrodes which are provided in a headrest provided on a seat of avehicle for sensing capacitances between a head of a human body sittingon the seat and the headrest, the sensing electrodes being provided sideby side along a height direction of the headrest; a detecting circuitwhich detects capacitance values which are based on the capacitancesfrom the plurality of sensing electrodes; and distance measuring meanswhich measures an electrode-head distance indicating a distance betweenthe headrest and the head, in accordance with detection results detectedby the detecting circuit, wherein when the sensing electrode located ata highest position of the headrest or the sensing electrode located at alowest position thereof among the plurality of sensing electrodes doesnot show a largest capacitance, the distance measuring means measuresthe electrode-head distance by calculating, on a two-dimensionalcoordinate system representing positions of the plurality of sensingelectrodes on its one axis and the capacitance values detected by thedetecting circuit on its other axis, a distance calculation angle formedby a line which connects a point representing the position andcapacitance value of the sensing electrode from which a largestcapacitance value is detected and a point representing the position andcapacitance value of the sensing electrode from which a smallestcapacitance value is detected among the sensing electrodes located abovethe sensing electrode from which the largest capacitance value isdetected and a line which connects the point representing the positionand capacitance value of the sensing electrode from which the largestcapacitance value is detected and a point representing the position andcapacitance value of the sensing electrode from which a smallestcapacitance value is detected among the sensing electrodes located underthe sensing electrode from which the largest capacitance value isdetected, and when the sensing electrode located at the highest positionof the headrest or the sensing electrode located at the lowest positionthereof shows the largest capacitance, the distance measuring meansmeasures the electrode-head distance by calculating, on thetwo-dimensional coordinate system, an angle of a slope of a line whichconnects a point representing the position and capacitance value of thesensing electrode from which a smallest capacitance value is detectedand a point representing the position and capacitance value of thesensing electrode from which a largest capacitance value is detected.

For example, the distance measuring means may obtain a first distancecalculation angle formed by the line which connects the pointrepresenting the sensing electrode located at the highest position andthe point representing the sensing electrode from which the largestcapacitance value is detected and a base line which extends to the oneaxis perpendicularly to the one axis from the point representing thesensing electrode from which the largest capacitance value is detectedand a second distance calculation angle formed by the line whichconnects the point representing the sensing electrode located at thelowest position and the point representing the sensing electrode fromwhich the largest capacitance value is detected and the base line, andmay calculate the distance calculation angle based on these first andsecond distance calculation angles.

For example, the distance measuring means may measure the electrode-headdistance by comparing the distance calculation angle with preset datawhich profiles a relationship between distance and angle.

For example, the plurality of sensing electrodes may be provided in theheadrest at a portion closer to a front surface of the headrest andformed in a rectangular strip shape having its longer dimension extendin a width direction perpendicular to the height direction, and thedetecting circuit may include a plurality of capacitance sensingcircuits which are connected one-to-one to the plurality of sensingelectrodes, and output capacitance values which are based on thecapacitances sensed by the sensing electrodes.

For example, the plurality of sensing electrodes may be provided in theheadrest at a portion closer to a front surface of the headrest andformed in a rectangular strip shape having its longer dimension extendin a width direction perpendicular to the height direction, and thedetecting circuit may include a switching circuit connected to theplurality of sensing electrodes, and a capacitance sensing circuit whichoutputs a capacitance value which is based on the capacitance sensed byany of the sensing electrodes which are to be connected theretointertemporally through the switching circuit.

A headrest position adjusting device according to the present inventionincludes: the device for measuring a distance between a headrest and ahead according to any of the inventions described above; and positionadjusting means which adjusts a position of the headrest to anappropriate position for the head based on a measurement result from thedevice for measuring a distance.

For example, based on the distance calculation angle which is includedin the measurement result, the position adjusting means may adjust theposition of the headrest by moving the headrest in a frontward directionor rearward direction of the vehicle in the manner that the distancecalculation angle becomes a predetermined angle.

For example, the position adjusting means may compare the distancecalculation angle included in the measurement result with apredetermined threshold, and when the distance calculation angle islarger than the predetermined threshold, may stop a position adjustingoperation for the headrest at least in the height direction.

For example, when the position adjusting means stops the positionadjusting operation for the headrest for a predetermined time, after thepredetermined time passes, the position adjusting means may againcompare the distance calculation angle with the predetermined threshold.

For example, when the distance calculation angle included in themeasurement result is larger than a predetermined threshold, theposition adjusting means may adjust the position of the headrest bymoving the headrest in an upward direction or downward direction of thevehicle by using the capacitance values which are detected by thedetecting circuit based on the capacitances from at least the sensingelectrode located at the highest position and the sensing electrodelocated at the lowest position among the plurality of sensingelectrodes.

When the distance calculation angle included in the measurement resultis equal or smaller than a predetermined threshold, the positionadjusting means may calculate an appropriate position of the headrestwith respect to the head by using the capacitance values which aredetected by the detecting circuit based on the capacitances from theplurality of sensing electrodes, and may adjust the position of theheadrest to the appropriate position.

A method for measuring a distance between a headrest and a headaccording to the present invention includes: a sensing step of sensingcapacitances between a head of a human body sitting on a seat of avehicle and a headrest provided on the seat by means of a plurality ofsensing electrodes which are provided in the headrest side by side alonga height direction of the headrest; a detecting step of detectingcapacitance values which are based on the capacitances sensed in thesensing step; and a distance measuring step of measuring anelectrode-head distance indicating a distance between the headrest andthe head, in accordance with detection results detected in the detectingstep, wherein when the sensing electrode located at a highest positionof the headrest or the sensing electrode located at a lowest positionthereof among the plurality of sensing electrodes does not show alargest capacitance, the distance measuring step measures theelectrode-head distance by calculating, on a two-dimensional coordinatesystem representing positions of the plurality of sensing electrodes onits one axis and the capacitance values detected in the detecting stepon its other axis, a distance calculation angle formed by a line whichconnects a point representing the position and capacitance value of thesensing electrode located at the highest position of the headrest and apoint representing the position and capacitance value of the sensingelectrode from which a largest capacitance value is detected and a linewhich connects a point representing the position and capacitance valueof the sensing electrode located at the lowest position of the headrestand the point representing the position and capacitance value of thesensing electrode from which the largest capacitance value is detected,and when the sensing electrode located at the highest position of theheadrest or the sensing electrode located at the lowest position thereofshows the largest capacitance, the distance measuring step measures theelectrode-head distance by calculating, on the two-dimensionalcoordinate system, an angle of a slope of a line which connects thepoint representing the position and capacitance value of the sensingelectrode located at the highest position of the headrest and the pointrepresenting the position and capacitance value of the sensing electrodelocated at the lowest position of the headrest.

A method for measuring a distance between a headrest and a headaccording to the present invention includes: a sensing step of sensingcapacitances between a head of a human body sitting on a seat of avehicle and a headrest provided on the seat by means of a plurality ofsensing electrodes which are provided in the headrest side by side alonga height direction of the headrest; a detecting step of detectingcapacitance values which are based on the capacitances sensed in thesensing step; and a distance measuring step of measuring anelectrode-head distance indicating a distance between the headrest andthe head, in accordance with detection results detected in the detectingstep, wherein the distance measuring step measures the electrode-headdistance by calculating, on a two-dimensional coordinate systemrepresenting positions of the plurality of sensing electrodes on its oneaxis and the capacitance values detected in the detecting step on itsother axis, an angle of a slope of a line which connects a pointrepresenting the position and capacitance value of the sensing electrodefrom which a smallest capacitance value is detected among the pluralityof sensing electrodes and a point representing the position andcapacitance value of the sensing electrode from which a largestcapacitance value is detected among the plurality of sensing electrodes.

A method for measuring a distance between a headrest and a headaccording to the present invention includes: a sensing step of sensingcapacitances between a head of a human body sitting on a seat of avehicle and a headrest provided on the seat by means of a plurality ofsensing electrodes which are provided in the headrest side by side alonga height direction of the headrest; a detecting step of detectingcapacitance values which are based on the capacitances sensed in thesensing step; and a distance measuring step of measuring anelectrode-head distance indicating a distance between the headrest andthe head, in accordance with detection results detected in the detectingstep, wherein when the sensing electrode located at a highest positionof the headrest or the sensing electrode located at a lowest positionthereof among the plurality of sensing electrodes does not show alargest capacitance, the distance measuring step measures theelectrode-head distance by calculating, on a two-dimensional coordinatesystem representing positions of the plurality of sensing electrodes onits one axis and the capacitance values detected in the detecting stepon its other axis, a distance calculation angle formed by a line whichconnects a point representing the position and capacitance value of thesensing electrode from which a largest capacitance value is detected anda point representing the position and capacitance value of the sensingelectrode from which a smallest capacitance value is detected among thesensing electrodes located above the sensing electrode from which thelargest capacitance value is detected and a line which connects thepoint representing the position and capacitance value of the sensingelectrode from which the largest capacitance value is detected and apoint representing the position and capacitance value of the sensingelectrode from which a smallest capacitance value is detected among thesensing electrodes located under the sensing electrode from which thelargest capacitance value is detected, and when the sensing electrodelocated at the highest position of the headrest or the sensing electrodelocated at the lowest position thereof shows the largest capacitance,the distance measuring step measures the electrode-head distance bycalculating, on the two-dimensional coordinate system, an angle of aslope of a line which connects a point representing the position andcapacitance value of the sensing electrode from which a smallestcapacitance value is detected and a point representing the position andcapacitance value of the sensing electrode from which a largestcapacitance value is detected.

For example, the distance measuring step may obtain a first distancecalculation angle formed by the line which connects the pointrepresenting the sensing electrode located at the highest position andthe point representing the sensing electrode from which the largestcapacitance value is detected and a base line which extends to the oneaxis perpendicularly to the one axis from the point representing thesensing electrode from which the largest capacitance value is detectedand a second distance calculation angle formed by the line whichconnects the point representing the sensing electrode located at thelowest position and the point representing the sensing electrode fromwhich the largest capacitance value is detected and the base line, andmay calculate the distance calculation angle based on these first andsecond distance calculation angles.

For example, the distance measuring step may measure the electrode-headdistance by comparing the distance calculation angle with preset datawhich profiles a relationship between distance and angle.

A headrest position adjusting method according to the present inventionincludes: the method for measuring a distance between a headrest and ahead according to any of the inventions described above; and a positionadjusting step of adjusting a position of the headrest to an appropriateposition for the head based on a measurement result measured by themethod for measuring a distance.

For example, based on the distance calculation angle which is includedin the measurement result, the position adjusting step adjusts theposition of the headrest by moving the headrest in a frontward directionor rearward direction of the vehicle in a manner that the distancecalculation angle becomes a predetermined angle.

For example, the position adjusting step may compare the distancecalculation angle included in the measurement result with apredetermined threshold, and when the distance calculation angle islarger than the predetermined threshold, may stop a position adjustingoperation for the headrest at least in the height direction.

For example, when the position adjusting step stops the positionadjusting operation for the headrest for a predetermined time, after thepredetermined time passes, the position adjusting step may again comparethe distance calculation angle with the predetermined threshold.

For example, when the distance calculation angle included in themeasurement result is larger than a predetermined threshold, theposition adjusting step may adjust the position of the headrest bymoving the headrest in an upward direction or downward direction of thevehicle by using the capacitance values which are detected in thedetecting step based on the capacitances from at least the sensingelectrode located at the highest position and the sensing electrodelocated at the lowest position among the plurality of sensingelectrodes.

For example, when the distance calculation angle included in themeasurement result is equal to or smaller than a predeterminedthreshold, the position adjusting step may calculate an appropriateposition of the headrest with respect to the head by using thecapacitance values which are detected in the detecting step based on thecapacitances from the plurality of sensing electrodes, and may adjustthe position of the headrest to the appropriate position.

Effect of the Invention

According to the present invention, it is possible to measure thedistance between a headrest and a head with a simple configuration andautomatically adjust the position of the headrest accurately bypreventing an unnecessary movement of the headrest.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of a seat of a vehiclemounted with a headrest position adjusting device including a device formeasuring the distance between a headrest and a head according to oneembodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of how the devicefor measuring the distance between the headrest and a head is disposedin the headrest according to one embodiment of the present invention.

FIG. 3 is a block diagram showing an example of the whole configurationof the distance measuring device.

FIG. 4 is a block diagram showing an example of configuration of acapacitance sensing circuit of the distance measuring device.

FIG. 5 is an operation waveform chart showing examples of operationwaveforms of a detecting circuit of the distance measuring device.

FIG. 6A is an explanatory diagram showing an example of outputs ofsensing electrodes of a distance measuring device according to oneembodiment of the present invention.

FIG. 6B is an explanatory diagram showing an example of outputs ofsensing electrodes of a distance measuring device according to oneembodiment of the present invention.

FIG. 6C is an explanatory diagram showing an example of outputs ofsensing electrodes of a distance measuring device according to oneembodiment of the present invention.

FIG. 7A is an explanatory diagram explaining a relationship between adistance calculation angle and an electrode-head distance according tothe distance measuring device.

FIG. 7B is an explanatory diagram explaining a relationship between adistance calculation angle and an electrode-head distance according tothe distance measuring device.

FIG. 8 is a flowchart showing one example of procedures of a distancemeasuring process by a method of measuring the distance between aheadrest and a head according to one embodiment of the presentinvention.

FIG. 9 is an explanatory diagram explaining a second example of outputsof sensing electrodes of a distance measuring device according to oneembodiment of the present invention.

FIG. 10A is an explanatory diagram explaining a third example of outputsof sensing electrodes of a distance measuring device according to oneembodiment of the present invention.

FIG. 10B is an explanatory diagram explaining a third example of outputsof sensing electrodes of a distance measuring device according to oneembodiment of the present invention.

FIG. 10C is an explanatory diagram explaining a third example of outputsof sensing electrodes of a distance measuring device according to oneembodiment of the present invention.

FIG. 11 is a block diagram showing another example of the wholeconfiguration of a device for measuring the distance between a headrestand a head according to one embodiment of the present invention.

FIG. 12 is a flowchart showing an example of procedures of a positionadjusting process by a headrest position adjusting method according toone embodiment of the present invention.

FIG. 13 is a flowchart for explaining another example of procedures of aposition adjusting process by a headrest position adjusting methodaccording to one embodiment of the present invention.

FIG. 14 is a flowchart showing still another example of procedures of aposition adjusting process by a headrest position adjusting methodaccording to one embodiment of the present invention.

FIG. 15A is an explanatory diagram showing an example of outputs ofsensing electrodes of a headrest position adjusting device according toone embodiment of the present invention.

FIG. 15B is an explanatory diagram showing an example of outputs ofsensing electrodes of a headrest position adjusting device according toone embodiment of the present invention.

FIG. 16 is an explanatory diagram explaining a relationship between anamount of movement of a headrest and an amount of change of outputaccording to the headrest position adjusting device.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of a device for measuring the distance between aheadrest and a head, a method for measuring the distance between aheadrest and a head, a headrest position adjusting device, and aheadrest position adjusting method according to the present inventionwill now be explained below with reference to the attached drawings.

FIG. 1 is a schematic diagram showing an example of a seat of a vehiclemounted with a headrest position adjusting device including a device formeasuring the distance between a headrest and a head according to oneembodiment of the present invention. FIG. 2 is an explanatory diagramshowing an example of how the device for measuring the distance betweenthe headrest and a head is disposed in the headrest according to oneembodiment of the present invention.

As shown in FIG. 1 and FIG. 2, a headrest position adjusting device 100is provided in a seat 40 of a vehicle, etc., and includes, for example,a distance measuring device 10 provided in a headrest front portion 43 cconstituting a part of a headrest 43 of the seat 40, and a drive motorunit 30 provided in a headrest back portion 43 d constituting anotherpart of the headrest 43. The distance measuring device 10 and the drivemotor unit 30 are electrically connected to each other through, forexample, a harness 29.

The headrest front portion 43 c is connected to the headrest backportion 43 d through a support shaft 43 b in a manner freely movable inthe frontward-rearward direction of the vehicle. The headrest backportion 43 d is connected to a backrest (a back sheet) 41 of the seat 40through a support shaft 43 a in a manner freely movable in theupward-downward direction (the height direction of the headrest 43) andthe leftward-rightward direction of the vehicle.

For example, the distance measuring device 10 includes a plurality ofsensing electrodes 11 to 15 formed on one surface (front surface) of asubstrate 19, and a detecting circuit 20 formed (mounted) on the othersurface (back surface) of the substrate 19. The distance measuringdevice 10 detects capacitance values based on capacitances from thesensing electrodes 11 to 15, detects a head 49 a of a human body 49sitting on a sitting portion 42 of the seat 40, and measures anelectrode-head distance indicating the distance between the headrestfront portion 43 c and the head 49 a.

The substrate 19 is made of, for example, a flexible printed board, arigid substrate, or a rigid flexible substrate. The plurality of sensingelectrodes 11 to 15 are made of a conductive material such as copper, acopper alloy, aluminum, etc. which is patterned on the substrate 19 madeof an insulating material such as polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyimide (PI), polyamide (PA), an epoxyresin, etc. Other than this, the plurality of sensing electrodes 11 to15 may be made of a material such as an electric wire, a conductivefilm, etc.

The plurality of sensing electrodes 11 to 15 are provided in theheadrest front portion 43 c at a portion close to the front surfacethereof, formed in a rectangular strip shape having its longer dimensionextend in the width direction (leftward-rightward direction) of theheadrest 43 perpendicular to the height direction of the headrest 43,and arranged side by side with their widths lined up along the heightdirection of the headrest 43. Electrode numbers 1 to 5 (N1 to N5 or ch1to ch5) are allocated to the plurality of sensing electrodes 11 to 15respectively. In the present example, there are provided fiveelectrodes, but it is only necessary to provide such a number ofelectrodes as are necessary for sensing a capacitance between the head49 a of the human body 49 sitting on the seat 40 and the headrest 43while the headrest 43 is at rest. For example, it is enough if there areprovided two or more electrodes.

As will be described in detail later, the distance measuring device 10generates on a virtual calculation region, a two-dimensional coordinatesystem representing the positions of the plurality of sensing electrodes11 to 15 on its one axis and detected capacitance values on its otheraxis, based on the capacitance values detected by the measurement. Then,on this two-dimensional coordinate system, the distance measuring device10 generates a line AB which connects a point A (see FIGS. 6A to 6C; thesame applies hereinafter) representing the position and capacitancevalue of the sensing electrode (e.g., the sensing electrode 15) locatedat the highest position of the headrest front portion 43 c among theplurality of sensing electrodes 11 to 15 and a point B (see FIGS. 6A to6C; the same applies hereinafter) representing the position andcapacitance value of the sensing electrode (e.g., the sensing electrode13) having detected the largest capacitance value.

The distance measuring device 10 generates a line CB which connects apoint C (see FIGS. 6A to 6C; the same applies hereinafter) representingthe position and capacitance value of the sensing electrode (e.g., thesensing electrode 11) located at the lowest position of the headrestfront portion 43 c and a point B representing the position andcapacitance value of the sensing electrode (e.g., the sensing electrode13) having detected the largest capacitance value. The distancemeasuring device 10 calculates an angle formed by the line AB and theline CB generated on the two-dimensional coordinate system as a distancecalculation angle θ (see FIGS. 6A to 6C; the same applies hereinafter),and measures the electrode-head distance based on the distancecalculation angle θ.

As shown in FIG. 3, the detecting circuit 20 of the distance measuringdevice 10 includes a plurality of capacitance sensing circuits 21 to 25which are connected one-to-one to the sensing electrodes 11 to 15 andoutput information indicating the capacitances sensed by the sensingelectrodes 11 to 15. The detecting circuit 20 also includes anarithmetic processing circuit 28 which is connected to the capacitancesensing circuits 21 to 15, calculates the distance calculation angle θand the electrode-head distance based on the capacitances indicated bythe information output by the capacitance sensing circuits 21 to 15,calculates the height position of the head 49 a by comparing thecapacitances, and outputs information regarding the calculation resultsto a motor driving circuit (unillustrated) of the drive motor unit 30.

The plurality of capacitance sensing circuits 21 to 15 generate pulsesignals having duty ratios which change in accordance with thecapacitances between the sensing electrodes 11 to 15 and the head 49 a,smooth the pulse signals, and output them as sensing signals. Thearithmetic processing circuit 28 includes, for example, a CPU, a RAM, aROM, etc., calculates the distance calculation angle θ andelectrode-head distance described above by using capacitance valueswhich are based on sensing signals from the capacitance sensing circuits21 to 25, calculates, for example, the height position of the head 49 a,and outputs a control signal, which is information based on thecalculation results, to at least the drive motor unit 30 configured tochange the position of the headrest front portion 43 c.

Here, as shown in FIG. 4, for example, each capacitance sensing circuit21 (22 to 25) has a duty ratio which changes in accordance with acapacitance C, and for example, includes a trigger signal generatingcircuit 101 which outputs a trigger signal TG having a fixed period, atimer circuit 102 which outputs a pulse signal Po having a duty ratiowhich changes in accordance with the level of the capacitance Cconnected to an input terminal, and a low-pass filter (LPF) 103 whichsmoothes the pulse signal Po.

For example, the timer circuit 102 includes two comparators 201 and 202,an RS flip-flop circuit (hereinafter referred to as “RS-FF”) 203 whichreceives the outputs of these comparators 201 and 202 at its resetterminal R and its set terminal S respectively, a buffer 204 whichoutputs an output DIS of the RS-FF 203 to the LPF 103, and a transistor205 which is controlled between on and off according to the output DISof the RS-FF 203.

The comparator 202 compares such a trigger signal TG as shown in FIG. 5which is output from the trigger signal generating circuit 101 with apredetermined threshold Vth2 divided by resistors R1, R2, and R3, andoutputs a set pulse synchronized with the trigger signal TG. This setpulse sets the Q output of the RS-FF 203.

The Q output as a discharge signal DIS turns off the transistor 205, andelectrically charges between the sensing electrode 11 (12 to 15) and theground (GND) at a speed defined by a time constant set by the to-groundcapacitance C of the sensing electrode 11 (12 to 15) and a resistor R4connected between the input terminal and a power supply line.Accordingly, the potential of an input signal Vin rises at a speeddefined by the capacitance C.

When the input signal Vin exceeds a threshold Vth1 defined by theresistors R1, R2, and R3, the output of the comparator 201 is inverted,thereby inverting the output of the RS-FF 203. As a result, thetransistor 205 is turned on, and the charges accumulated in the sensingelectrode 11 (12 to 15) are discharged through the transistor 205.

Hence, the timer circuit 102 outputs a pulse signal Po which, as shownin FIG. 5, oscillates at a duty ratio that is based on the capacitance Cbetween the sensing electrodes 11 (12 to 15) and the head 49 a of thehuman body 49 coming close to the sensing electrode. The LPF 103 outputsa direct-current sensing signal Vout shown in FIG. 5 by smoothing thepulse signal Po. In FIG. 5, a waveform indicated by a solid line and awaveform indicated by a dotted line show that the former has a smallercapacitance than that of the latter, and, for example, the latterrepresents a condition that an object is coming close.

The drive motor unit 30 includes a motor driving circuit which changesthe position of the headrest 43 by controlling an unillustrated drivemotor based on a control signal which is based on calculation results ofthe arithmetic processing circuit 28 which has performed calculations inthe detecting circuit 20 of the distance measuring device 10 based onsensing signals Vout from the capacitance sensing circuits 21 to 25. Thedrive motor unit 30 also includes a drive motor which actually moves theposition of the headrest 43 under the control of the motor drivingcircuit.

In the present example, the drive motor unit 30 adjusts at least theheadrest front portion 43 c by causing a movement (frontward-rearwardmovement) of the headrest front portion 43 c in the frontward directionor rearward direction of the vehicle based on a measurement result ofthe distance measuring device 10. That is, by using the electrode-headdistance included in the measurement result, the drive motor unit 30causes a following movement of the headrest front portion 43 c such thatthe headrest 43 c comes at a fixed distance from the head 49 a.

Specifically, the drive motor is configured to drive the support shaft43 b of the headrest front portion 43 c to freely move in thefrontward-rearward direction and drive the support shaft 43 a of theheadrest back portion 43 d to freely move in the upward-downwarddirection and the leftward-rightward direction (i.e., to make anupward-downward/leftward-rightward movement). Hence, the headrestposition adjusting device 100 according to the present example canadjust the headrest 43 to an appropriate position for the head 49 a bycausing not only a frontward-rearward movement of the headrest 43described above but an upward-downward/leftward-rightward movementthereof.

The headrest position adjusting device 100 configured as described abovecan perform position adjustment for the headrest 43 based on ameasurement result which includes the distance (electrode-head distance)between the head 49 a and the headrest 43, which is obtained by thesensing electrodes 11 to 15 of the distance measuring device 10 sensingcapacitances C with respect to the head 49 a and the detecting circuit20 calculating the distance calculation angle θ, etc. based on thevalues of the capacitances.

FIGS. 6A, 6B, and 6C are explanatory diagrams showing examples ofoutputs of the sensing electrodes of the distance measuring deviceaccording to one embodiment of the present invention. FIGS. 7A and 7Bare diagrams explaining a relationship between the distance calculationangle and the electrode-head distance of the distance measuring device.For example, as shown in FIG. 6A, when the height-direction centerposition of the head 49 a is defined as P and a to-electrode distancefrom this center position P, which exists within an electrode-electrodedistance H, to each of the sensing electrodes 11 to 15 is defined as L,a value (capacitance value) to be output on a two-dimensional coordinatesystem D will be as follows.

That is, for example, when the electrode-head distance L is equal to orless than a predetermined range and the vicinity of the side-by-sidearrangement direction center of the sensing electrodes 11 to 15 (or thevicinity of the center of the headrest front portion 43 c) and thecenter position P of the head 49 a face each other substantiallyhorizontally, the output value of the sensing electrode 13 is thelargest of the output values of the sensing electrodes 11 to 15 and theoutput values of the sensing electrodes 15 and 11 which are located atthe highest position or the lowest position of the headrest frontportion 43 c are the smallest.

In this case, the distance measuring device 10 generates on thetwo-dimensional coordinate system D, a line AB which connects a point Arepresenting the position and output value of the sensing electrode 15located at the highest position and a point B representing the positionand output value of the sensing electrode 13 from which the largestoutput value is detected. The distance measuring device 10 alsogenerates a line BC which connects a point C representing the positionand output value of the sensing electrode 11 located at the lowestposition and the point B representing the position and output value ofthe sensing electrode 13 from which the largest output value isdetected.

Hence, the distance measuring device 10 can obtain a distancecalculation angle θ determined by the two lines AB and CB and can derivean electrode-head distance L determined by the obtained distancecalculation angle θ by comparing the distance calculation angle θ withsuch data as shown in FIG. 7 which profiles a relationship betweendistance and angle. The distance calculation angle θ can also beobtained by calculating a first distance calculation angle θ1 formed bythe line AB and a base line 13L which extends from the point B to theaxis representing the positions of the sensing electrodesperpendicularly to this axis and a second distance calculation angle θ2formed by the base line BL and the line CB and combining these angles.

That is, for example, when the largest output value of the output valuesof the sensing electrodes 11 to 15 is defined as V_(max), the numberallocated to the sensing electrode which corresponds to this valueV_(max), is extracted as N_(max), the output value of the sensingelectrode 15 (N₅) is defined as V₅, and the output value of the sensingelectrode 11 (N₁) is defined as V₁, the angles θ1 and θ2 can becalculated by the following formulae (1) and (2).

$\begin{matrix}{\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\mspace{625mu}} & \; \\{\theta_{1} = {\tan^{- 1}\left( \frac{N_{\max} - N_{5}}{V_{\max} - V_{5}} \right)}} & (1) \\{\left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\mspace{625mu}} & \; \\{\theta_{2} = {\tan^{- 1}\left( \frac{N_{1} - N_{\max}}{V_{\max} - V_{1}} \right)}} & (2)\end{matrix}$

Then, the distance calculation angle θ can be obtained by calculatingθ=θ1+θ2. For example, there is a case when the largest output value isthe output value of the sensing electrode 11 as shown in FIG. 6B, giventhat the electrode-head distance L is equal to or less than apredetermined range and the vicinity of the sensing electrode 11 locatedat the lowest position and the center position P of the head 49 a faceeach other substantially horizontally.

In this case, a line BCC0 which connects the zero point C0 of the outputvalue of the sensing electrode 11 and the point (the point representingthe largest output value) BC and a line ABC which connects this point BCand the point A representing the position and output value of thesensing electrode 15 located at the highest position form a distancecalculation angle θ (a first distance calculation angle θ1 or the slopeof the line ABC (an acute angle) θ1).

On the other hand, there is a case when the largest output value is theoutput value of the sensing electrode 15 as shown in FIG. 6C, giventhat, for example, the electrode-head distance L is equal to or lessthan a predetermined range and the vicinity of the sensing electrode 15located at the highest position and the center position P of the head 49a face each other substantially horizontally. In this case, a line ABA0which connects the zero point A0 of the output value of the sensingelectrode 15 and the point (the point representing the largest outputvalue) AB and a line ABC which connects this point AB and the point Crepresenting the position and output value of the sensing electrode 11located at the lowest position form a distance calculation angle θ (asecond distance calculation angle θ2 or the slope of the line ABC (anacute angle) θ2).

As shown in FIG. 7A, the first distance calculation angle θ1 or thesecond distance calculation angle θ2 which can be obtained in this wayexhibits a relationship of becoming larger as the electrode-headdistance L becomes larger, as represented by a correlation curve T1.Likewise, as shown in FIG. 7B, the distance calculation angle θ exhibitsa relationship of becoming larger as the electrode-head distance Lbecomes larger, as represented by a correlation curve T2.

Accordingly, the distance measuring device 10 according to the presentexample can measure the electrode-head distance L by letting thearithmetic processing circuit 28 of the detecting circuit 20 use thisdistance calculation angle θ (including the first and second distancecalculation angles θ1 and θ2; the same applies hereinafter). Then, theheadrest position adjusting device 100 including this distance measuringdevice 10 adjusts the position of the headrest 43 to an appropriateposition for the head 49 a based on the measurement result obtained bythe distance measuring device 10.

FIG. 8 is a flowchart showing one example of procedures of a distancemeasuring process by the method of measuring the distance between theheadrest and the head according to one embodiment of the presentinvention. As shown in FIG. 8, first, the distance measuring device 10detects capacitance values which are based on capacitances sensed by thesensing electrodes 11 to 15 with respect to the head 49 a (step S10).

Next, the distance measuring device 10 extracts the largest output value(peak output value) from among the detected capacitance values (stepS11), and generates an output map by mapping the output values on such atwo-dimensional coordinate system D as described above which representsthe positions of the sensing electrodes 11 to 15 on its one axis andcapacitance values on its other axis (step S12).

Then, the distance measuring device 10 calculates the distancecalculation angle θ in the way described above (step S13), andcalculates the electrode-head distance L by, for example, comparing thecalculated distance calculation angle θ with data profiling arelationship between distance and angle (step S14) thereby to measurethe actual distance between the headrest 43 and the head 49 c.

FIG. 9 is an explanatory diagram explaining a second example of outputsof the sensing electrodes of the distance measuring device according toone embodiment of the present invention. FIGS. 10A, 10B, and 10C areexplanatory diagrams explaining third examples of outputs of the sensingelectrode of the distance measuring device according to one embodimentof the present invention. Aside from the way described above withreference to FIGS. 6A to 6C, the distance measuring device 10 may alsoobtain the distance calculation angle θ in the following way, forexample. That is, as shown in FIG. 9, the distance measuring device 10generates a line EF which connects a point E representing the positionand output value of the sensing electrode 12 from which the smallestoutput value is detected among the plurality of sensing electrodes 11 to15 and a point F representing the position and output value of thesensing electrode 14 from which the largest output value is detected.

The distance measuring device 10 also generates a line FF0 whichconnects the zero point F0 of the output value of the sensing electrode14 and the point F to form a distance calculation angle θ by the line EFand the line FF0, and measures the electrode-head distance L. In thiscase, since the distance calculation angle θ is equal to the acute-angleslope of the line EF, the distance measuring device 10 can obtain thedistance calculation angle θ by calculating the angle of this slope.

Alternatively, as shown in FIG. 10A, when neither the sensing electrode15 located at the highest position nor the sensing electrode 11 locatedat the lowest position shows the largest output value, the distancemeasuring device 10 may generate a line JK which connects a point Jrepresenting the position and output value of the sensing electrode 14from which the largest output value is detected and a point Krepresenting the position and output value of the sensing electrode 15from which the smallest output value is detected among the sensingelectrodes located above the sensing electrode 14.

Then, the distance measuring device 10 may generate a line JM whichconnects the point J representing the sensing electrode 14 and a point Mrepresenting the position and output value of the sensing electrode 12from which the smallest output value is detected among the sensingelectrodes located under the sensing electrode 14 to form a distancecalculation angle θ by the line JK and the line JM and thereby measurethe electrode-head distance L.

Alternatively, as shown in FIG. 10B, when either the sensing electrode15 located at the highest position or the sensing electrode 11 locatedat the lowest position shows the largest output value (here, the sensingelectrode 11 does), the distance measuring device 10 may generate a lineUV which connects a point U representing the position and output valueof the sensing electrode 14 from which the smallest output value isdetected and a point V representing the position and output value of thesensing electrode 11 from which the largest output value is detected.The distance measuring device 10 may also generate a line VV0 whichconnects the zero point V0 of the output value of the sensing electrode11 and the point V to form a distance calculation angle θ by the line UVand the line VV0 and thereby measure the electrode-head distance L. Alsoin this case, since the distance calculation angle θ is equal to theacute-angle slope of the line UV, the distance measuring device 10 canobtain the distance calculation angle θ by calculating the angle of thisslope.

Still alternatively, as shown in FIG. 10C, when either the sensingelectrode 15 located at the highest position or the sensing electrode 11located at the lowest position shows the largest output value (here, thesensing electrode 15 does), the distance measuring device 10 maygenerate a line RS which connects a point R representing the positionand output value of the sensing electrode 12 from which the smallestoutput value is detected and a point S representing the position andoutput value of the sensing electrode 15 from which the largest outputvalue is detected. The distance measuring device 10 may also generate aline SS0 which connects the zero point S0 of the output value of thesensing electrode 15 and the point S to form a distance calculationangle θ by the line RS and the line SS0 and thereby measure theelectrode-head distance L. Also in this case, since the distancecalculation angle θ is equal to the acute-angle slope of the line RS,the distance measuring device 10 can obtain the distance calculationangle θ by calculating the angle of this slope.

FIG. 11 is a block diagram showing another example of the wholeconfiguration of a device for measuring the distance between a headrestand a head according to one embodiment of the present invention. In thefollowing description, any portions that are the same as those alreadyexplained will be denoted by the same reference numerals and explanationthereof will not be provided. As shown in FIG. 11, the detecting circuit20 includes a switching circuit 26 connected to the sensing electrodes11 to 15, a capacitance sensing circuit 27 which outputs informationindicating a capacitance sensed by any of the sensing electrodes 11 to15 which are to be connected thereto intertemporally through theswitching circuit 26, and an arithmetic processing circuit 28 whichcalculates a distance calculation angle θ, an electrode-head distance L,etc. based on the information output by the capacitance sensing circuit27 and outputs information indicating the calculation result to themotor driving circuit of the drive motor unit 30.

This configuration of the detecting circuit 20 allows the distancemeasuring device 10 to be configured with a minimum number ofcapacitance sensing circuits, and enables the electrode-head distance Lto be obtained by calculating the distance calculation angle θ based ona result of sequentially scanning the capacitances of the respectivesensing electrodes 11 to 15 which are switched among them by theswitching circuit 26.

FIG. 12 is a flowchart showing an example of procedures of a positionadjusting process by a headrest position adjusting method according toone embodiment of the present invention. Because the headrest positionadjusting device 100 described above includes the distance measuringdevice 10 as part of its configuration, the arithmetic processingcircuit 28 of the detecting circuit 20 has a function as a control unitfor controlling the entire headrest position adjusting device 100 and afunction as distance measuring means and position adjusting means. Here,a position adjusting process for adjusting the headrest 43 in thefrontward-rearward direction will be explained.

As shown in FIG. 12, first, the headrest position adjusting device 100judges whether or not the process is to be started as triggered by, forexample, an ignition switch of the vehicle being turned to an accessorystate or an ON state (step S100). When it is judged that the process isnot to be started (step S100; N), the headrest position adjusting device100 terminates the series of position adjusting process according tothis flowchart.

When it is judged that the process is to be started (step S100; Y), thedistance measuring device 10 performs the distance measuring processdescribed above (step S101), and obtains the measurement result (stepS102). Then, the headrest position adjusting device 100 judges whetheror not the distance calculation angle θ included in the measurementresult is equal to or larger than, for example, a predetermined angleshown in the above-described data profiling a relationship betweendistance and angle (step S103). Note that the predetermined angle may bepreset to an angle which defines a distance that is the most preferableas the electrode-head distance L (i.e., the optimum distance to the head49 a).

When it is judged that the distance calculation angle θ is equal to orlarger than the predetermined angle (step S103; Y), the headrestposition adjusting device 100 calculates the difference between theelectrode-head distance L defined by the distance calculation angle θand the distance defined by the predetermined angle, and controls thedrive motor unit 30 to move the headrest front portion 43 c frontward byan amount of the calculated difference (step S104). When it is judgedthat the distance calculation angle θ is smaller than the predeterminedangle (step S103; N), the headrest position adjusting device 100calculates the difference likewise, and moves the headrest front portion43 c rearward by an amount of the calculated difference (step S105).

After the headrest front portion 43 c is moved, the headrest positionadjusting device 100 judges whether or not the process is to beterminated by, for example, the ignition switch of the vehicle beingturned OFF (step S106), and when it is judged that the process is to beterminated (step S106; Y), terminates the series of position adjustingprocess according to the present flowchart. When it is judged that theprocess is not to be terminated (step S106; N), the headrest positionadjusting device 100 goes to step S101 described above and repeats thesubsequent process.

By performing the position adjusting process in this way, it is possibleto perform position adjustment by using the measurement result obtainedby the distance measuring device 10 and causing a frontward/rearwardfollowing movement of the headrest front portion 43 c with respect tothe position of the head 49 a. At step S103 described above, comparisonis made between the distance calculation angle θ and the predeterminedangle. However, for example, comparison may be made between theelectrode-head distance L determined by the distance calculation angle θand the optimum distance described above to go on to step S104 or stepS105 described above.

FIG. 13 is a flowchart showing another example of procedures of aposition adjusting process by a headrest position adjusting methodaccording to one embodiment of the present invention. Here, a positionadjusting process for adjusting the headrest 43 in the upward-downwarddirection will be explained. The process from step S110 to step S112 ofthe present flowchart is the same as the process from step S100 to stepS102 described above, and hence explanation thereof will not beprovided.

As shown in FIG. 13, the headrest position adjusting device 100 judgeswhether or not the distance calculation angle θ included in themeasurement result is larger than a predetermined threshold (forexample, a predetermined angle shown in the above-described dataprofiling a relationship between distance and angle) (step S113). Whenit is judged that the distance calculation angle θ is larger than thepredetermined threshold (step S113; Y), which means that it is possibleto judge that the electrode-head distance L is greater than apredetermined range, the headrest position adjusting device 100 stopsthe position adjusting operation for the headrest back portion 43 d inthe height direction (step S114) and waits until a predetermined timepasses (step S115; N).

On the other hand, when it is judged that the distance calculation angleθ is equal to or smaller than the predetermined threshold (step S113;N), which means that it is possible to judge that the electrode-headdistance L is equal to or less than the predetermined range, theheadrest position adjusting device 100 calculates the height position ofthe head 49 a by using the capacitance values included in themeasurement result (step S117), and performs the position adjustingoperation for the headrest back portion 43 d in the height direction(step S118).

Note that at step S117, the headrest position adjusting device 100calculates the height position of the head 49 a based on the capacitancevalues included in the measurement result obtained by all of the sensingelectrodes 11 to 15 of the distance measuring device 10. For example,the headrest position adjusting device 100 calculates a position that isestimated to be the height-direction center of the head 49 a (anestimated center position) by comparing these capacitance values, andcalculates the height position of the head 49 a based on this estimatedcenter position.

When the predetermined time has passed (step S115; Y) or when theposition adjusting operation has been completed (step S118), theheadrest position adjusting device 100 judges whether or not the processis to be terminated (step S116), and when it is judged that the processis to be terminated (step S116; Y), terminates the series of positionadjusting process according to the present flowchart. When it is judgedthat the process is not to be terminated (step S116; N), the headrestposition adjusting device 100 goes to step S111 described above andrepeats the subsequent process.

By performing the position adjusting process in this way, it is possibleto perform position adjustment by using the measurement result obtainedby the distance measuring device 10 and moving the headrest back portion43 d in the upward-downward direction. When the electrode-head distanceL is greater than the predetermined range (i.e., when the electrodes aredistanced from the head 49 a), the position adjusting process stops theheight-direction position adjusting operation for the headrest backportion 43 d. This can to prevent an unnecessary movement of theheadrest 43, avoid giving discomfort to the occupant (vehicle occupant)as much as possible, and suppress unnecessary power consumption.

FIG. 14 is a flowchart showing still another example of procedures of aposition adjusting process by a headrest position adjusting methodaccording to one embodiment of the present invention. The process fromstep S120 to step S123 of the present flowchart is the same as theprocess from step S110 to step S113 described above, and henceexplanation thereof will not be provided.

As shown in FIG. 14, when it is judged that the distance calculationangle θ included in the measurement result is larger than apredetermined threshold (for example, a predetermined angle shown in theabove-described data profiling a relationship between distance andangle) (step S123; Y), the headrest position adjusting device 100 canjudge that the electrode-head distance L is greater than a predeterminedrange.

Hence, the headrest position adjusting device 100 compares thecapacitance value of the sensing electrode located at the highestposition (for example, the sensing electrode 15) and the capacitancevalue of the sensing electrode located at the lowest position (forexample, the sensing electrode 11) based on the measurement result (stepS124) to calculate the height position of the head 49 a. On the otherhand, when it is judged that the distance calculation angle θ is equalto or smaller than the predetermined threshold (step S123; N), theheadrest position adjusting device 100 can judge that the electrode-headdistance L is equal to or less than the predetermined range.

Hence, the headrest position adjusting device 100 calculates the heightposition of the head 49 a by comparing the capacitance values of all ofthe sensing electrodes 11 to 15 based on the measurement result (stepS125). After this, the headrest position adjusting device 100 performs aheight-direction position adjusting operation for the headrest backportion 43 d based on the calculation result of step S124 or step S125(step S 126).

When the position adjusting operation has been completed, the headrestposition adjusting device judges whether or not the process is to beterminated (step S127). The headrest position adjusting device 100terminates the series of position adjusting process according to thepresent flowchart when it is judged that the process is to be terminated(step S 127; Y), or goes to step S121 described above and repeats thesubsequent process when it is judged that the process is not to beterminated (step S 127; N).

Here, comparison among the capacitance values of the sensing electrodes11 to 15 which are included in the measurement result results inobtaining a capacitance change amount ΔC which is based on the outputsof the sensing electrodes 11 to 15. This capacitance change amount ΔCbecomes unsuitable as the information for obtaining the height positionof the head 49 a when the electrode-head distance L becomes greater thana predetermined range, because in this case, there are onlyinsignificant differences among the outputs, making it difficult toperform position adjustment.

However, comparison between the capacitance value of the sensingelectrode 15 located at the highest position and the capacitance valueof the sensing electrode 11 located at the lowest position results asfollows. That is, even when the electrode-head distance L is greaterthan the predetermined range, an output change amount ΔV (mV) based onthe outputs A and B of the sensing electrodes 15 and 11 shows that thedifference between the outputs is insignificant when the height of thecenter position P of the head 49 a is substantially equal to the heightof the center of the headrest 43 as shown in FIG. 15A, but that thedifference is significant otherwise as shown in FIG. 15B.

Based on the output change amount ΔV obtained in this way, an outputratio α between the output B of the sensing electrode 11 and the outputA of the sensing electrode 15 can be obtained as α=B/(A+B) as shown inFIG. 16. An amount (mm) to move the headrest (H/R) can be calculatedbased on the obtained output ratio α.

Accordingly, given that the amount to move when the height of the centerposition P of the head 49 a is horizontally equal to the height of thecenter of the headrest 43 is 0 mm, a control signal is output to thedrive motor unit 30 to move the headrest back portion 43 d upward (in a“+” direction) when the output ratio α is close to 0, or to move theheadrest back portion 43 d downward (in a “−” direction) when the outputratio α is close to 1.

In this way, the headrest position adjusting device 100 according to thepresent example can obtain the position of the head 49 a through thestep S124 described above based on the capacitance values of the sensingelectrodes 15 and 11 located at the highest and lowest positions whenthe distance calculation angle θ is larger than the predeterminedthreshold and hence the electrode-head distance L is greater than thepredetermined range, or through step S125 described above based on thecapacitance values of the sensing electrodes 11 to 15 when the distancecalculation angle θ is equal to or smaller than the predeterminedthreshold and hence the electrode-head distance L is equal to or lessthan the predetermined range. Therefore, the headrest position adjustingdevice 100 can adjust the position of the headrest 43 highly accuratelywith a simple configuration, and can prevent accidents due to failure toadjust the position of the headrest 43, such as cervical spine injury ofthe human body 49 in a car crash, etc.

At step S113 and step S123 described above, comparison is made betweenthe distance calculation angle θ and the predetermined threshold.However, for example, comparison may be made between the electrode-headdistance L determined by the distance calculation angle θ and theoptimum distance described above to perform the subsequent process.

The above-described embodiment has explained that position adjustment isperformed by moving the headrest front portion 43 c or the headrest backportion 43 d in the frontward-rearward direction or in theupward-downward direction through the position adjusting processes shownin FIGS. 12 to 14. However, position adjustment may be performed by, forexample, executing these processes in parallel based on the measurementresult obtained from the distance measuring device 10, such that theposition of the headrest 43 may be adjusted to a position that isappropriate for the head 49 a in all of the frontward-rearward,upward-downward, and leftward-rightward directions.

The distance measuring device 10 may measure the electrode-head distanceL by letting the arithmetic processing circuit 28 select a preset slopecoefficient for the distance calculation angle θ based on the sensingelectrode from which the largest output value is measured among thesensing electrodes 11 to 15 and compare the slope coefficient with theangle.

The distance measuring device 10 may include, for example, three sensingelectrodes which are located at the highest position, the lowestposition, and the middle portion between these positions of the headrestfront portion 43 c, and measure the electrode-head distance L bycalculating the distance calculation angle θ based on the capacitancevalues of these sensing electrodes.

DESCRIPTION OF REFERENCE NUMERALS

10 distance measuring device

11 to 15 sensing electrode

19 substrate

20 detecting circuit

21 to 25 capacitance sensing circuit

26 switching circuit

27 capacitance sensing circuit

28 arithmetic processing circuit

29 harness

30 drive motor unit

40 seat

41 backrest (seat back)

42 sitting portion

43 headrest

43 a support shaft

43 b support shaft

43 c headrest front portion

43 d headrest back portion

49 human body

49 a head

100 headrest position adjusting device

The invention claimed is:
 1. A device for measuring a distance between aheadrest and a head, comprising: a plurality of sensing electrodes whichare provided in a headrest provided on a seat of a vehicle for sensingcapacitances between a head of a human body sitting on the seat and theheadrest, the sensing electrodes being provided side by side along aheight direction of the headrest; a detecting circuit which detectscapacitance values which are based on the capacitances from theplurality of sensing electrodes; and distance measuring means whichmeasures an electrode-head distance indicating a distance between theheadrest and the head, in accordance with detection results detected bythe detecting circuit, wherein when the sensing electrode located at ahighest position of the headrest or the sensing electrode located at alowest position thereof among the plurality of sensing electrodes doesnot show a largest capacitance, the distance measuring means measuresthe electrode-head distance by calculating, on a two-dimensionalcoordinate system representing positions of the plurality of sensingelectrodes on its one axis and the capacitance values detected by thedetecting circuit on its other axis, a distance calculation angle formedby a line which connects a point representing the position andcapacitance value of the sensing electrode located at the highestposition of the headrest and a point representing the position andcapacitance value of the sensing electrode from which a largestcapacitance value is detected and a line which connects a pointrepresenting the position and capacitance value of the sensing electrodelocated at the lowest position of the headrest and the pointrepresenting the position and capacitance value of the sensing electrodefrom which the largest capacitance value is detected, and when thesensing electrode located at the highest position of the headrest or thesensing electrode located at the lowest position thereof shows thelargest capacitance, the distance measuring means measures theelectrode-head distance by calculating, on the two-dimensionalcoordinate system, an angle of a slope of a line which connects thepoint representing the position and capacitance value of the sensingelectrode located at the highest position of the headrest and the pointrepresenting the position and capacitance value of the sensing electrodelocated at the lowest position of the headrest.
 2. A device formeasuring a distance between a headrest and a head, comprising: aplurality of sensing electrodes which are provided in a headrestprovided on a seat of a vehicle for sensing capacitances between a headof a human body sitting on the seat and the headrest, the sensingelectrodes being provided side by side along a height direction of theheadrest; a detecting circuit which detects capacitance values which arebased on the capacitances from the plurality of sensing electrodes; anddistance measuring means which measures an electrode-head distanceindicating a distance between the headrest and the head, in accordancewith detection results detected by the detecting circuit, wherein thedistance measuring means measures the electrode-head distance bycalculating, on a two-dimensional coordinate system representingpositions of the plurality of sensing electrodes on its one axis and thecapacitance values detected by the detecting circuit on its other axis,an angle of a slope of a line which connects a point representing theposition and capacitance value of the sensing electrode from which asmallest capacitance value is detected among the plurality of sensingelectrodes and a point representing the position and capacitance valueof the sensing electrode from which a largest capacitance value isdetected among the plurality of sensing electrodes.
 3. A device formeasuring a distance between a headrest and a head, comprising: aplurality of sensing electrodes which are provided in a headrestprovided on a seat of a vehicle for sensing capacitances between a headof a human body sitting on the seat and the headrest, the sensingelectrodes being provided side by side along a height direction of theheadrest; a detecting circuit which detects capacitance values which arebased on the capacitances from the plurality of sensing electrodes; anddistance measuring means which measures an electrode-head distanceindicating a distance between the headrest and the head, in accordancewith detection results detected by the detecting circuit, wherein whenthe sensing electrode located at a highest position of the headrest orthe sensing electrode located at a lowest position thereof among theplurality of sensing electrodes does not show a largest capacitance, thedistance measuring means measures the electrode-head distance bycalculating, on a two-dimensional coordinate system representingpositions of the plurality of sensing electrodes on its one axis and thecapacitance values detected by the detecting circuit on its other axis,a distance calculation angle formed by a line which connects a pointrepresenting the position and capacitance value of the sensing electrodefrom which a largest capacitance value is detected and a pointrepresenting the position and capacitance value of the sensing electrodefrom which a smallest capacitance value is detected among the sensingelectrodes located above the sensing electrode from which the largestcapacitance value is detected and a line which connects the pointrepresenting the position and capacitance value of the sensing electrodefrom which the largest capacitance value is detected and a pointrepresenting the position and capacitance value of the sensing electrodefrom which a smallest capacitance value is detected among the sensingelectrodes located under the sensing electrode from which the largestcapacitance value is detected, and when the sensing electrode located atthe highest position of the headrest or the sensing electrode located atthe lowest position thereof shows the largest capacitance, the distancemeasuring means measures the electrode-head distance by calculating, onthe two-dimensional coordinate system, an angle of a slope of a linewhich connects a point representing the position and capacitance valueof the sensing electrode from which a smallest capacitance value isdetected and a point representing the position and capacitance value ofthe sensing electrode from which a largest capacitance value isdetected.
 4. The device for measuring a distance between a headrest anda head according to claim 1, wherein the distance measuring meansobtains a first distance calculation angle formed by the line whichconnects the point representing the sensing electrode located at thehighest position and the point representing the sensing electrode fromwhich the largest capacitance value is detected and a base line whichextends to the one axis perpendicularly to the one axis from the pointrepresenting the sensing electrode from which the largest capacitancevalue is detected and a second distance calculation angle formed by theline which connects the point representing the sensing electrode locatedat the lowest position and the point representing the sensing electrodefrom which the largest capacitance value is detected and the base line,and calculates the distance calculation angle based on these first andsecond distance calculation angles.
 5. The device for measuring adistance between a headrest and a head according to claim 3, wherein thedistance measuring means obtains a first distance calculation angleformed by the line which connects the point representing the sensingelectrode located at the highest position and the point representing thesensing electrode from which the largest capacitance value is detectedand a base line which extends to the one axis perpendicularly to the oneaxis from the point representing the sensing electrode from which thelargest capacitance value is detected and a second distance calculationangle formed by the line which connects the point representing thesensing electrode located at the lowest position and the pointrepresenting the sensing electrode from which the largest capacitancevalue is detected and the base line, and calculates the distancecalculation angle based on these first and second distance calculationangles.
 6. The device for measuring a distance between a headrest and ahead according to claim 1, wherein the distance measuring means measuresthe electrode-head distance by comparing the distance calculation anglewith preset data which profiles a relationship between distance andangle.
 7. The device for measuring a distance between a headrest and ahead according to claim 2, wherein the distance measuring means measuresthe electrode-head distance by comparing the distance calculation anglewith preset data which profiles a relationship between distance andangle.
 8. The device for measuring a distance between a headrest and ahead according to claim 3, wherein the distance measuring means measuresthe electrode-head distance by comparing the distance calculation anglewith preset data which profiles a relationship between distance andangle.
 9. A headrest position adjusting device, comprising: the devicefor measuring a distance between a headrest and a head according toclaim 1; and position adjusting means which adjusts a position of theheadrest to an appropriate position for the head based on a measurementresult from the device for measuring a distance.
 10. A headrest positionadjusting device, comprising: the device for measuring a distancebetween a headrest and a head according to claim 2; and positionadjusting means which adjusts a position of the headrest to anappropriate position for the head based on a measurement result from thedevice for measuring a distance.
 11. A headrest position adjustingdevice, comprising: the device for measuring a distance between aheadrest and a head according to claim 3; and position adjusting meanswhich adjusts a position of the headrest to an appropriate position forthe head based on a measurement result from the device for measuring adistance.
 12. The headrest position adjusting device according to claim9, wherein based on the distance calculation angle which is included inthe measurement result, the position adjusting means adjusts theposition of the headrest by moving the headrest in a frontward directionor rearward direction of the vehicle in a manner that the distancecalculation angle becomes a predetermined angle.
 13. The headrestposition adjusting device according to claim 10, wherein based on thedistance calculation angle which is included in the measurement result,the position adjusting means adjusts the position of the headrest bymoving the headrest in a frontward direction or rearward direction ofthe vehicle in a manner that the distance calculation angle becomes apredetermined angle.
 14. The headrest position adjusting deviceaccording to claim 11, wherein based on the distance calculation anglewhich is included in the measurement result, the position adjustingmeans adjusts the position of the headrest by moving the headrest in afrontward direction or rearward direction of the vehicle in a mannerthat the distance calculation angle becomes a predetermined angle. 15.The headrest position adjusting device according to claim 9, wherein theposition adjusting means compares the distance calculation angleincluded in the measurement result with a predetermined threshold, andwhen the distance calculation angle is larger than the predeterminedthreshold, stops a position adjusting operation for the headrest atleast in the height direction.
 16. The headrest position adjustingdevice according to claim 10, wherein the position adjusting meanscompares the distance calculation angle included in the measurementresult with a predetermined threshold, and when the distance calculationangle is larger than the predetermined threshold, stops a positionadjusting operation for the headrest at least in the height direction.17. The headrest position adjusting device according to claim 11,wherein the position adjusting means compares the distance calculationangle included in the measurement result with a predetermined threshold,and when the distance calculation angle is larger than the predeterminedthreshold, stops a position adjusting operation for the headrest atleast in the height direction.
 18. The headrest position adjustingdevice according to claim 9, wherein when the distance calculation angleincluded in the measurement result is larger than a predeterminedthreshold, the position adjusting means adjusts the position of theheadrest by moving the headrest in an upward direction or downwarddirection of the vehicle by using the capacitance values which aredetected by the detecting circuit based on the capacitances from atleast the sensing electrode located at the highest position and thesensing electrode located at the lowest position among the plurality ofsensing electrodes.
 19. The headrest position adjusting device accordingto claim 10, wherein when the distance calculation angle included in themeasurement result is larger than a predetermined threshold, theposition adjusting means adjusts the position of the headrest by movingthe headrest in an upward direction or downward direction of the vehicleby using the capacitance values which are detected by the detectingcircuit based on the capacitances from at least the sensing electrodelocated at the highest position and the sensing electrode located at thelowest position among the plurality of sensing electrodes.
 20. Theheadrest position adjusting device according to claim 11, wherein whenthe distance calculation angle included in the measurement result islarger than a predetermined threshold, the position adjusting meansadjusts the position of the headrest by moving the headrest in an upwarddirection or downward direction of the vehicle by using the capacitancevalues which are detected by the detecting circuit based on thecapacitances from at least the sensing electrode located at the highestposition and the sensing electrode located at the lowest position amongthe plurality of sensing electrodes.